Circuit breakers are commonly used for providing automatic circuit interruption upon detection of undesired overcurrent conditions on the circuit being monitored. These overcurrent conditions include, among others, overload conditions, ground faults and short-circuit conditions.
Circuit breakers typically include an electrical contact on a movable blade which rotates away from a stationary contact in order to interrupt the current path. The blade is pivotally mounted to a rotatable blade carrier, and a spring is used to bias the movable contact toward the stationary contact during normal current conditions. The type of overcurrent condition dictates how quickly the blade must rotate away from the stationary contact. For example, in response to overcurrent conditions at relatively low magnitudes but present for a long period of time, circuit breakers generally employ a tripping mechanism to rotate the blade carrier carrying the blade. Since the blade rotates with the blade carrier, the contact on the blade is forced away from the stationary contact. In response to overcurrent conditions at relatively high magnitudes, circuit breakers must break (or blow-open) the current path very quickly, reacting must faster than the reaction time for the tripping mechanism. In this case, the blade rotates to an open position prior to actuation of the tripping mechanism. The blade is maintained in the open position using a mechanism such as a blade catcher.
A drawback of the foregoing contact blade assembly is that in order to catch and maintain the blade in this open position, the circuit breaker requires a mechanism which is separate from the blade and the contact force-producing spring. It is difficult to properly coordinate the operation of this separate mechanism with the movement of the blade to successfully catch and maintain the blade in the open position. In addition, this separate mechanism increases the cost and complexity of the circuit breaker.
Accordingly, there is a need for a contact blade assembly for a circuit breaker which can be implemented without the aforementioned shortcomings.